What did I do wrong?

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  • Last Post 27 May 2009
LWesthoff posted this 23 March 2009

   When my supply(s) of lino looked to be drying up, I contacted a friend who is part owner of a small company that casts pistol bullets and bought 100+ lbs. of the alloy he uses.  It comes from a local foundry, and the stuff I got  was straight from the foundry, with their name cast right into the bars, and with the alloy composition (91-7-2) stamped on every bar.  I figured I'd try it for rifle bullets as is, and if they weren't hard enough, with 7% antimony content I could always heat treat the bullets and get them up to lino hardness or better.   Some time ago, I acquired a small toaster oven for just that purpose.

   The other day I cast a bunch of Lyman 311679 bullets using the 91-7-2 alloy, and decided to go ahead and do a trial heat treating run just to see what would happen.I selected 2 bullets, both from the same cavity, with no visible flaws and within 0.3 gr. weight.  I ran the toaster oven, set at 450 degrees, for about a half hour with my Lyman casting thermometer in it, checking the thermometer through the window to make sure the temperature didn't fluctuate too wildly.  As near as I could tell, it held at 440 degrees within +/- less than ten degrees.  I measured the length of the two bullets and wrote the measurement on each bullet with a “sharpie” pen.  Then I cooked one bullet at 440 for one hour (with an aluminum tray under it and a sheet of aluminum foil over it), opened the toaster oven door and immediately quenched the bullet in tap water.  It made a very gratifying hiss when it hit the water.

   I waited about 24 hours and then put the heat treated bullet and its un-heat treated companion base to base and squeezed them in a vise until I could see a visible shortening in the two bullets, and measured them again.

   The heat treated bullet had shortened 0.049".  The as-cast bullet had shortened only 0.042"!  Just backward!

   Somebody give me a hand here.  What did I do wrong?

 

  

 

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CB posted this 24 March 2009

Your HT oven was too hot, I think I only take mine up to about 325 - 350.. Past that the bullets may start to slump.

Check the diameter the length of the bullet, your answer may lie there..

Also you need some either arsenic or sulphur (the latter is easier to get a hold of) to modify the grainular structure of the lead alloy so HT will work. There is a post here somewhere that talks about that.

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CB posted this 24 March 2009

You're temp is right at around 440 degrees. You might try adding about 5% magnum shot to your mix since I doubt if you have any arsenic in it if it came from a foundry. I'd imagine 91-7-2 is about 17BNH so unless you plan on really pushing the bullet HTing might be a waste of time. One thing for certain is if you're going to start worrying about actual hardness you're going to have to buy a hardness tester

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LWesthoff posted this 24 March 2009

Thanks to all of you for your helpful replies. Sounds as though - for practical application - I need some arsenic (or maybe sulphur?) to get a successful heat treat, even though the literature I have available says it's not really necessary. Before I go that route, I'm going to shoot some of this stuff as-cast. If I can get no leading and accuracy comparable to lino, I'll quit worrying about heat treating. Otherwise, I may have to look into that sulpher idea. I live on 10 wooded acres out in the country and my casting bench is in my shop (an outbuilding) with a range hood and fan installed over the bench. The sulphur smell shouldn't do more than kill a vine maple or two, while cooking arsenic might kill something more important (like maybe the cook).

Wes

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RicinYakima posted this 24 March 2009

Even in Eatonville, you're safe from the arsenic! It will stay bound to the tin and antimony atoms at any temperature a commerial electrical pot will generate. It is the antimony dust from the fluxing that will get you if you don't keep your work area clean. Ric

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454PB posted this 26 March 2009

Heat treating takes a while to happen. Check that same mashed boolit in a week or two, you'll find it's harder than the hubs of hell.

Try dropping the freshly cast boolits directly into water rather than oven treating. It's not as consistent, but the difference in hardness is only about 2 to 3 BHN. Your alloy should harden to 25 to 28 BHN when water dropped.

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LWesthoff posted this 26 March 2009

Well, I started this; guess I ought to add an update. Loaded up 20 rounds with the un-heat treated (as-cast) 91-7-2 alloy bullets and shot 'em through my retired '06 hunting rifle at 100 yds. yesterday morning. (In case I was going to get some leading, I didn't want to have to clean it out of the rifles I use for competition.)

The hunting rifle is pretty light; if I don't hold it down on the rest and back against my shoulder pretty hard it tends to scatter a bit. The second target stayed just under 1.8” while the first target had 8 in 1.7” with a couple (that I think were my fault) that opened it up to 2.5". When I got home I ran a couple patches of Ed's Red through it and the following dry patches came out clean as a whistle. Looks like I don't have to worry about heat treating and that's good.

Ric, I know my pot won't get an arsenic/antimony alloy hot enough to boil out any arsenic fumes. I was referring to the idea that adding raw sulphur to the mix wouldn't do anything but raise a stink, but trying to add raw arsenic (assuming I could find some) might not be such a good idea.

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RicinYakima posted this 26 March 2009

I wish you would try the sulphur experiment. I read about it at the LASC sight, but don't know of anyone who has actually done it! Ric

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Rumplestiltskin posted this 27 May 2009

I'm having the same problem. I heat treated a handfull of .357 that measured ~14 BHN and now it's down to ~10 BHN! I'm guessing I had bad alloy, (wheelweights + 5% solder, water quenched) or maybe bad fluxing practice (parafin wax added to bottom pour, stirred, and dross scrapped off)? Maybe I need to add magnum shot next time? How much shot should be added to 20 lbs to add enough arsenic? Haven't actually fired any yet. Has this happened to anyone else, bullets getting SOFTER after heat treating?

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Ed Harris posted this 27 May 2009

Too much tin. Up to 2% doesn't hurt as long as there is at least as much Sb as Sn, so that it will be tied up in the intermetallic compound Sb-Sn. But you don't want need than about 1% Sn for fill out and as little as 1/2% is enough to provide boundary layer oxidation protection.

It doesn't take much As to aid precipitation in quench hardening. About 5 pounds of shot to a potful of alloy should be enough.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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jhalcott posted this 27 May 2009

OUCH! Ed, that's HALF my 10 pound pot! I only use a few ounces in a pot full of Wheel weights or lyman #2. Actually it is about 1500 grains as weighed on my scale. I don't often Heat Treat my bullets unless they are for very hi velocity or target work. The left over HT'ed bullets are used on ground hogs!

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JimmyDee posted this 27 May 2009

Ed Harris:  About 5 pounds of shot to a potful of alloy should be enough.

Say, Ed, how big is the pot you're using?

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CB posted this 27 May 2009

Yup, get your self a bag of Lawrence “Magnum” shot and add a couple of table spoons of this shot to 20# of alloy , there is your arsenic , no problem.

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